Arresting devices for falling bodies



July 2, 1963 G. E. LINDSAY ETAL ARRESTING DEVICES FOR FALLING BODIES Filed June 14, 1957 GRAHAM EADES LINDSAY SIDNEY JOHN J OSLIN WALDRON Inventors Attorneys ARRESTHNG DEVIQES FOR FALLING BODIES Graham Eades Lindsay, London, and Sidney John J slin Waldron, Harwell, England, assignors to United Klugdom Atomic Energy Authority, London, England Filed June 14, 1957, Ser. No. 665,812 Claims priority, application Great Britain June 14, 1956 3 (Ilaims. (Cl. 204-1932) This invention relates to arresting devices for falling bodies.

In a nuclear reactor having vertically suspended control or shut off rods, the possibility of the failure of the means supporting the control rods with consequent damage when the control rods fall has to be considered.

It is an object of the present invention toprovide means to arrest a falling body in one or more stages depending on the circumstances of the fall so that large impact forces are avoided.

According to the invention, a device for arresting a falling body comprises in combination with the body an impacting member, a vertically resilient means coupling the impacting member and the body yieldable linking means such as a coupling releasable when the load in the vertically resilient means exceeds a predetermined amount to allow the body to continue its fall free of the impacting member and energy dissipating means for finally arresting the body.

An arresting device in accordance with the invention will now be described with reference to the accompanying drawings. In the drawings:

FIG. 1 is an elevation of one part of the device.

FIG. 2 is an elevation in section of the other part of the device.

Referring to the drawings there is shown a control rod 1 which has associated with it an arresting device comprising two principal parts, first at the top of the control rod 1 (FIG. 1), a spring 2 which acts between an arrester cup 3 and a ring 4 secured to the control rod 1 via shear pins 5 and a control rod support head 6 of cylindrical form. Second (FIG. 2) at the bottom of the control rod a broaching arrester mechanism comprising an impact pin 7 carrying a broaching cutter 8 movable in a free cutting stainless steel liner 9 held within a body tube 10' mounted on the control rod 1.

Referring to FIG. 1 in more detail the control rod 1 is attached to the support head 6 by a shank 11 formed integral with the support head 6. The shank 11 is screwed in a threaded hole 12 in the upper end of the control rod 1. The support head 6 has an integral lifting eye 13 and a conical flange 14 divides the support head 6 from the shank 11. The arrester cup 3 has a conical impacting face 15 formed round its base. A hole 16 in the base of the cup 3 and an aperture 17 defined by a ring 18 welded to the upper end of the cup 3 allow it to slide on the support head 6 against the loading of the spring 2.

Considering FIG. 2 in more detail the body tube 10 of the broaching arrcster mechanism has an end adaptor 19 which is screwed into the lower end of the control rod 1. The free cutting stainless steel liner 9 is held within the body tube 10 between an internal end face 20 of the adaptor 19 and an internal end face 21 of a bearing sleeve 22 which is screwed into the lower end of the body 10. The liner 9 has internal grooves 30. The broaching cutter 8 is ring shaped and has six equally spaced external cutting edges. The cutter 8 is held within the liner 9 and its end 23 adjacent to the bearing sleeve and is fitted into the liner 9 by prebroaching the liner 9 fora short distance from the end 23. The broaching cutter 8 is carried by the impact pin 7 which has two parts, i.e., an upper part 24 bearing in the adaptor 19 and a lower part 25 bearing in the bearing sleeve 22. The broaching cutter 8 is carried on the part 24 of the impact pin 7 and rests against a step 26 between the two parts 24 and 25. The part 25 of the impact pin 7 projects from the bearing sleeve 22. A stop in the form of a washer 27 and a nut 28 is carried on the end 29 of the impact pin 7 where it projects from the adaptor 19.

The operation of the device will now be described with reference to the case of a control rod falling into a vertical control rod channel of a nuclear reactor from an initial position in which the control rod is suspended with its lower end passing through a hole in a charge pan situated on the top of the core of the reactor. At the start of the fall the conditions shown in the drawings apply.

The control rod 1 falls until the conical face 15 of the cup 3 hits a complementary face 31 formed around the edge of the hole in the charge pan through which the control rod 1 is falling. The cup 3 is thus arrested by the charge pan and the kinetic energy of the falling control rod 1 is absorbed as the compression spring 2 is compressed between the cup 3 and the ring 4 carried by the support head 6. The load which is set up in the compression spring 2 is taken by the shear pins 5 which couple the ring 4 with the support head 6. If this load now exceeds an amount determined by the shear strength of the shear pins 5 they fail and the control rod 1 and associated support head 6 fall away from the cup 3, compression spring 2 and ring 4. The control rod 1 then continues to fall freely until the downwardly projecting impact pin 7 of the broach strikes an impact stool 32 situated at the foot of the control rod channel. The im pact pin 7 is arrested by the impact stool 32 and due to the impact the broaching cutter 8 is forced along the liner 9.

The liner 9 is cut as the broaching cutter 8 is forced along it and as the kinetic energy of the falling control rod 1 is dissipated in the broaching operation the control rod 1 is finally decelerated to rest.

It will be seen that if the control rod 1 falls from a position such that the cup 3 receives only a moderate impact on being arrested by the charge pan the shock of the fall will be absorbed in the compression spring 2 without fracture of the shear pins 5 and the control rod 1 will be arrested at this point with no damage. However, if the impact is more serious, damage is confined to the shear pins 5 and the liner 9 which can easily be replaced. The liner 9 is provided with internal grooves 30 to ensure that the cuttings produced are in the form of chippings which will not cause jamming of the breach.

We claim:

1. A body adapted to be suspended vertically and to extend through an aperture in a fixed structure having an upper complementary face and a lower impact stool, a support head fixed to the upper end of said body, an arrester cup having an inner vertical bore through which said support head extends, said arrester cup having a face on its outer surface adapted to engage with said complementary face for arresting the fall of said arrester cup, vertically resilient means fixed inside said arrester cup, yieldable linking means connecting said support head to said resilient means and adapted to yield and release said support head and body to fall free of the cup and resilient means when the force across said linking means increases to a predetermined magnitude, and energy absorbing means at the lower end of said body adapted to engage with said lower impact stool to absorb the energy of the free fall of said support head and body.

2. The apparatus claimed in claim 1 wherein said means at the lower end of said body for absorbing the energy of free fall comprises an impact pin, a broaching cutter carried by the impact pin and held within a free cutting References Cited in the file of this patent UNITED STATES PATENTS Kuller Oct. 24, 1911 Pegard Oct. 28, 1952 Reynolds May 26, 1953 Butler Oct. 26, 1957 Greenhalgh et al Mar. 10, 1959 

1. A BODY ADAPTED TO BE SUSPENDED VERTICALLY AND TO EXTEND THROUGH AN APERTURE IN A FIXED STRUCTURE HAVING AN UPPER COMPLEMENTARY FACE AND A LOWER IMPACT STOOL, A SUPPORT HEAD FIXED TO THE UPPER END OF SAID BODY, AN ARRESTER CUP HAVING AN INNER VERTICAL BORE THROUGH WHICH SAID SUPPORT HEAD EXTENDS, SAID ARRESTER CUP HAVING A FACE ON ITS OUTER SURFACE ADAPTED TO ENGAGE WITH SAID COMPLEMENTARY FACE FOR ARRESTING THE FALL OF SAID ARRESTER CUP, VERTICALLY RESILIENT MEANS FIXED INSIDE SAID ARRESTER CUP, YIELDABLE LINKING MEANS CONNECTING SAID SUPPORT HEAD TO SAID RESILIENT MEANS AND ADAPTED TO YIELD AND RELEASE SAID SUPPORT HEAD AND BODY TO FALL FREE OF THE CUP AND RESILIENT MEANS WHEN THE FORCE ACROSS SAID LINKING MEANS INCREASES TO A PREDETERMINED MAGNITUDE, AND ENERGY ABSORBING 